This invention relates to the field of subterranean drilling. Typically, downhole hammers are used to affect periodic mechanical impacts upon a drill bit. Through this percussion, the drill string is able to more effectively apply drilling power to the formation, thus aiding penetration into the formation.
The prior art has addressed the operation of a downhole tool actuated by drilling fluid. Such issues have been addressed in the U.S. Pat. No. 4,979,577 to Walter, which is herein incorporated by reference for all that it contains. The '577 patent discloses a low pulsing apparatus that is adapted to be connected in a drill string above a drill bit. The apparatus includes a housing providing a passage for a flow of drilling fluid toward the bit. A valve which oscillates in the axial direction of the drill string periodically restricts the flow through the passage to create pulsations in the flow and a cyclical water hammer effect thereby to vibrate the housing and the drill bit during use. Drill bit induced longitudinal vibrations in the drill string can be used to generate the oscillation of the valve along the axis of the drill string to effect the periodic restriction of the flow or, in another form of the invention, a special valve and spring arrangement is used to help produce the desired oscillating action and the desired flow pulsing action.